The present invention relates to an improved apparatus for the supervision or correction of electrical signals, the apparatus including a plurality of signal channels which carry signals comparable to one another and which are connected by way of a mean value-forming means or circuit to an evaluation or correcting circuit. Apparatus of this kind is generally referred to by the designation "mean value-forming redundancy circuit."
When for example a plurality of input signals are to be supervised by means of an apparatus of this kind, a mean value signal is formed from the input signals and each input signal is compared with this mean value signal. Too great a difference between an input signal and the mean value signal is taken as denoting that the input signal concerned is faulty and brings about its exclusion from the process of mean value formation. Here the decisive factor for determining a fault is the comparatively smaller error component within the mean value signal.
It is a disadvantage of this known apparatus that an abrupt alteration of an input signal brought about by a fault, initially appears -- disregarding the attenuation brought about by mean value formation -- in the mean value signal passed on for further processing, until the fault is recognized by comparison of the respective input signal with the mean value signal and the faulty input signal is disconnected. A further disadvantage consists in that a fault which may occur in another input signal still further weakens the difference criterion relevant for the fault and, in a system with three input signals, the fault detection becomes impossible.